Make cleartool location configurable.
Review Request #2047 — Created Dec. 2, 2020 and submitted
In some cases, the cleartool executable may be in an unusual location, have an alternate name, or users may want to use a wrapper script of some sort. This change adds an optional settings key to allow people to set the location or name of cleartool. Testing Done: Ran unit tests. Reviewed at https://reviews.reviewboard.org/r/11290/